Mold release compositions have long been used to facilitate the release of molded polymer parts from molds. Particularly in the case of parts having complex shapes or deep sections, and more particularly in the case of polymers which display aggressive adhesion to the mold surface, production of parts without an effective mold release would not be possible.
A wide variety of mold releases exist. Early mold releases relied on natural and synthetic waxes. Often, molds would have to be hand or machine buffed to obtain maximum release. Such mold release agents are not practical for modern high speed production rates. One advantage of such mold releases, however, is that they are often paintable without wiping or cleaning, and can be readily removed as well.
Aqueous soap solutions and dispersions are sometimes used as mold releases. However, soaps are not highly effective, and cannot be used with moisture sensitive molding compositions such as polyurethane RIM unless allowed to thoroughly dry. If still moist, surface defects and local foaming may occur in polyurethane RIM.
Polyurethane RIM has been especially problematic due to its natural tendency to adhere to molds. A considerable advance in RIM technology was the introduction of internal mold releases based on zinc stearate in conjunction with fatty substances such as fatty esters and epoxidized natural oils. These mold releases are incorporated into the reactive composition prior to molding. Unfortunately, in order to provide consistent, multiple releases, such internal mold releases must be used at high levels. For parts which must be painted, these high levels of use impair paintability. Decreasing the amount of internal mold release, however, increases the difficulty of release. Thus, such systems generally employ external mold releases in conjunction with internal mold releases.
Organopolysiloxanes such as trimethylsiloxy-terminated polydimethylsiloxane fluids have proven to be effective mold release agents, and when used in conjunction with aminoalkyl and thioalkyl-functional organopolysiloxanes, as disclosed in U.S. Pat. Nos. 4,251,277 and 3,883,628 provide extraordinary release.
Such organopolysiloxane fluids can be applied neat, in solution in organic solvent, or in the form of an aqueous emulsion. For pigmented moldings such as ski boots, roller blades, and the like, such mold releases are exemplary. Unfortunately, polydimethylsiloxane fluids are notorious for destroying paintability of molded parts, even after extensive wiping and washing operations. Common paint defects include uneven coverage, sometimes to the extent of large bare areas, orange peel, runs, sags, and particularly, fish eyes. The effects of such fluids on paintability is so severe, that some manufacturing plants ban all products containing polydimethylsiloxanes, even solid silicones such as gasketing material. Suppliers of O-ring seals and other products must frequently certify that their products contain no polydimethylsiloxanes.
Efforts to retain the advantages of polydimethylsiloxanes as mold release agents while retaining paintability have been only partially successful. Modification of these siloxanes by replacing a portion of the methyl groups with relatively hydrophobic hydrocarbon groups, e.g. C.sub.4-30 alkyl groups, phenyl groups, and in particular, with .alpha.-methylphenylethyl groups, has resulted in siloxane mold releases which are sometimes paintable immediately after demolding and without further post treatment such as wiping or washing, and which rather uniformly display good paintability after such post treatment. An example of such fluids is Wacker TN available from Wacker Silicones, Adrian, Mich. Similar mold releases are disclosed by Japanese Kokai JP 09012886 A2.
Unfortunately, while exhibiting enhanced paintability, the aforementioned modified siloxanes are not nearly as efficient in their mold release properties as straight polydimethylsiloxanes that contain aminoorgano- or thiolorgano-functional organopolysiloxane. This is particularly the case where deep sections and/or aggressively adhering polymer systems are involved.
It would be desirable to provide a mold release composition which is comparable in ease of mold release with polydimethylsiloxanes that contain aminoorgano- or thiolorgano-functional organopolysiloxane(s), while being paintable as well.